Xe is used as assist gas in semiconductor production processes such as the plasma etching process. Xe is not consumed by reaction, etc. during the process, and is discharged as waste gas with water, carbon dioxide (CO2) and such reaction products as fluorohydrocarbons (FC) such as CHF3, CF4, C2F6 and C2F4. Since Xe is extremely expensive and a rare element, retrieval and recycle of Xe in waste gases have been demanded.
For retrieving Xe, it is desirable to collect the waste gas from a section that does not affect the semiconductor process. Specifically, if the waste gas is collected from the downstream of the detoxification device (detoxifies carbon monoxide (CO), fluorine (F2), hydrogen fluoride (HF), etc. by combustion, catalytic reaction or adsorption) of reactive gases located at the downstream of the semiconductor production process, it is possible to avoid affecting the semiconductor production process. However, since the waste gas collected from this section contained only approximately 0.1˜1 vol. % (hereinafter referred to as “%”) of Xe, and approximately the equivalent concentration of other substances such as water, CO2, and FC as impurities, there was a technological problem to be overcome. In other words, to retrieve and concentrate Xe from a section that does not negatively affect the process, it is necessary not only to efficiently retrieve and concentrate low-concentration Xe but also to efficiently remove impurities such as water, CO2 and FC.
Some technologies to retrieve and recycle noble gases such as Xe from such semiconductor production processes have previously been reported. Specifically, the following proposals can be listed.
(1) Methods of separating and refining high-added-value gases (noble gases) from waste gases by combining the pressure variable adsorption separation method (PSA) and velocity type pressure variable adsorption separation method (refer to patent document 1, for example).
(2) Noble gases retrieval devices that retrieve noble gases contained in waste gases discharged from facilities that use noble gases, retrieve the noble gases by at least 2 or more gas separation processes, and use the retrieved gases by returning them to the noble gas supply line of the facilities that use noble gases (refer to patent document 2, for example).
(3) Refinement methods characterized by separating halogenated hydrocarbon by low-temperature adsorption from waste gases discharged from facilities that use noble gases (refer to patent document 4, for example).
(4) Devices that separate, refine, recycle and reuse high-added-value gases (noble gases) by introducing methods, using PSA, to remove minor gas components such as helium (He) and hydrogen (H2) that are normally difficult to separate from waste gases containing high-added-value gases (noble gases) such as krypton (Kr) and Xe (refer to patent document 4, for example).    [Patent document 1] Patent published unexamined application 2002-126435    [Patent document 2] Patent published unexamined application 2002-097007    [Patent document 3] Patent published unexamined application 2003-062419    [Patent document 4] Patent published unexamined application 2005-246137